Founded in 1958 by James How, a trained engineer and viola student, Rotosound is a British string manufacturer based in Sevenoaks, Kent, England. The company originated as Orchestral & Jazz Strings before adopting the Rotosound name — derived from the Latin word roto (round) — to reflect its pioneering work in roundwound string technology. The brand's defining moment came in 1966 when John Entwistle of The Who visited the factory seeking a heavy, even-sounding roundwound bass string, leading to the development of the RS66 Swing Bass 66 — a stainless steel roundwound set that became one of the most influential bass strings in rock history.

Rotosound manufactures all of its strings in England and remains a family-run business. Its product range spans electric guitar strings (Rotos, British Steels, Pure Nickels), bass strings (Swing Bass 66, Jazz Bass 77 monel flatwounds, Solo Bass 55, Tru Bass 88 black nylon tapewounds), acoustic strings (Jumbo King, Super Bronze), and strings for traditional instruments including violin, banjo, mandolin, and ukulele. The company also produces effects pedals, including a reissue of a vintage fuzz pedal, along with accessories such as capos, tuners, and guitar care products.

Rotosound strings have been used by a wide range of prominent musicians across genres, including Jimi Hendrix, Roger Waters, John Paul Jones, Geddy Lee, Steve Harris, Duff McKagan, Joe Dart, Guthrie Govan, and Billy Sheehan. Steve Harris's use of Jazz Bass 77 flatwounds is a key part of his signature tone in Iron Maiden, while the Swing Bass 66 set developed with John Entwistle helped define the aggressive, growling bass sound of early rock. A fictional Rotosound jingle appeared on The Who's 1967 album The Who Sell Out.

Rotosound has 82 products cataloged on Equipboard, including Strings, Fuzz Effects Pedals, and Univibe & Rotary Effects Pedals. Their gear is featured by 131 artists, with the strongest followings in Rock, Pop, and Electronic. Notable users include Duff McKagan, Billy Sheehan, and Danny Sapko.